This proposal will perform a comprehensive assessment of the characteristics of the vaso-occlusive pain experience in infants and young children with Sickle Cell Disease (SCD). It will be the first study to specifically characterize the pain intensity and duration of both outpatient and hospital-treated painful episodes, with a prospective design, in a large population of infants and young children. In addition, this study will examine several other facets of the pain experience in these patients that have not been previously studied in any depth, including possible precipitating factors, behavioral response to pain, and analgesic usage and efficacy. In collaboration with Project I, we will comprehensively examine the relationship between hematologic and laboratory variables and the onset and frequency of pain in these infants and young children. We will also conduct the first detailed study of the validity and reliability of available pain assessment instruments in this patient population, and examine the relationship between pain frequency and infant temperament or parental coping style. While each one of these studies could be done in isolation, the combination of these studies in the same patient population, on a prospective basis, will yield a wealth of comparative information that will allow us to assess the relative importance of a comprehensive set of clinical and laboratory factors that predict the risk for painful episodes, the most frequent and debilitating complication of SCD. With the knowledge obtained from the above studies, we will be better able to alleviate the pain and suffering of these patients through more effective pain assessment and management. More importantly, we will be able to identify at an early age, prior to the onset of major organ damage, those children with frequent clinical complications who could be appropriate candidates for trials of innovate therapies for SCD.